Fibrous webs, particularly low basis weight webs between 8 and 50 lbs. per ream (3,000 sq. ft.), for use ultimately as tissue, towel and napkin products, are fabricated conventionally by two alternate processes. The older wet laid process dispenses an aqueous slurry of pulped paper-making fibers, typically natural cellulose fibers, from a headbox onto a moving foraminous support means, e.g., a fourdrinier wire, the aqueous medium being removed through the support means by vacuum means. The wet laid web is thermally dried and taken up on a parent roll. Because of the presence of water, the wet laid web fibers bond naturally to one another by means of hydrogen bonding. Furthermore, the high water content of the wet laid web, which decreases from about 99% by weight beneath the headbox to between about 35 to 50% just prior to consolidation, facilitates densification of the web. The water "lubricates" the web so that the individual fibers can come into close physical relationship with one another. The result is a densified web of low bulk, but having good absorbency.
The second, now conventional, yet relatively recent, process defiberizes cellulose pulp, the dry individual fibers being pneumatically transported to the dispensing means, and then dry laid (or air laid) onto the moving foraminous support means. Vacuum means below the support means is employed to ensure that the dry fibers remain in the web, which web has little inherent strength inasmuch as hydrogen bonds are not formed in the absence of an aqueous medium. The dry, initially laid web is then sprayed with a synthetic bonding agent, such as a latex emulsion, preferably on both surfaces of the web. The bonding agent is cured by passing the thus treated web though a dryer, e.g., a through air dryer, before being taken up on a parent roll.
The bonding agent characteristically is a hydrophobic substance, that is antagonistic to water, and of limited solubility in water. The bonding agent permeates the web, and encapsulates a major portion of the otherwise hydrophilic fibers. Notwithstanding the thus diminished absorbency capabilities of dry laid webs, these products have certain advantageous properties. The high bulk reduces the amount of fiber per ream (3000 sq. ft.) of paper product, and the presence of the bonding material increases wet strength, making these products particularly useful as industrial or heavy duty wipes. The dry laid process also permits better formation of the fibrous matrix, thereby improving softness and aesthetic appeal. Thus, it is apparent that dry laid products have a distinct absorbency disadvantage as compared to their wet laid counterparts even though superior in other aspects.